pressure reducing valve - which pipe should it fit on??

[lavenders19]

I have a Vokera compact 24 and the was advised to fit a pressure reducing valve. Where should this go? Is it for the central heating side or the dhw side?

Thanks in advance for any comments.

[BigWallop]

It's usually fitted to the water supply pipe, before the fill loop if this side of the system too is giving problems.